[PATCH 4/4] ALSA: usb-audio: Add dB scale quirk for Xiaomi Speaker Mini

From: Rong Zhang

Date: Mon Oct 19 2026 - 16:24:14 EST

I recently brought an Xiaomi Speaker Mini (USB Product string, marketing
name: Xiaomi Bluetooth Speaker Mini), which is never advertised as UAC
capable.

By chance, I connected it to my PC, and a UAC device showed up.
Unsurprisingly, it's yet another device with insane volume control, so I
tried to measure its volume mapping @ 1000Hz with a microphone:

+--------+--------+-----------+-------------+--------+
| hex | dec | dec => dB | measured dB | res |
+--------+--------+-----------+-------------+--------+
| 0xd000 | -12288 | -48.00 | (mute) | |
| 0xdd00 | -8960 | -35.00 | -68.6 | 3328 # |
| 0xe540 | -6848 | -26.75 | -61.2 | 2112 |
| 0xea40 | -5568 | -21.75 | -57.0 | 1280 |
| 0xed80 | -4736 | -18.50 | -52.5 | 832 |
| 0xf0a0 | -3936 | -15.38 | -48.3 | 800 |
| 0xf2d0 | -3376 | -13.19 | -42.1 | 560 |
| 0xf4d0 | -2864 | -11.19 | -36.1 | 512 |
| 0xf6c0 | -2368 | -9.25 | -32.0 | 496 |
| 0xf840 | -1984 | -7.75 | -24.0 | 384 |
| 0xf9e0 | -1568 | -6.13 | -17.9 | 416 |
| 0xfb30 | -1232 | -4.81 | -13.9 | 336 |
| 0xfc80 | -896 | -3.50 | -10.0 | 336 |
| 0xfd90 | -624 | -2.44 | -6.0 | 272 |
| 0xfeb0 | -336 | -1.31 | -4.0 | 288 |
| 0xffb0 | -80 | -0.31 | -2.0 | 256 |
| 0x0000 | 0 | 0.00 | 0.0 | 80 |
+--------+--------+-----------+-------------+--------+

Footnote #: running out of the 10-item limit of TLV ranges. The
limitation is from alsa-lib, where MAX_TLV_RANGE_SIZE == 256 Bytes.

The volume control mixer declares res == 256, but actually acts like
res == 1 (i.e., accepts any value between min and max) and has uneven
resolutions in reality. Setting any value between (0xd000, 0xdd00]
results in the same audible volume as 0xdd00, and so on.

Carefully overrides cval->{min,max,res} so that volume steps with
2dB or 4dB resolution can be approximately represented togother.
With that, we can expose a 25-step TLV range mapping with 10 items.

The quirk is applied only when the mixer values match the seen ones,
so that it won't be accidentally applied to unseen variants.

Quirky device sample:

usb 3-1: new full-speed USB device number 14 using xhci_hcd
usb 3-1: New USB device found, idVendor=2717, idProduct=5096, bcdDevice= 1.00
usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 3-1: Product: Xiaomi Speaker Mini-****
usb 3-1: Manufacturer: bestechnic
usb 3-1: SerialNumber: 20160406.1
usb 3-1: Found last interface = 0
usb 3-1: 1:1: add audio endpoint 0x3
usb 3-1: Creating new data endpoint #3
usb 3-1: 1:1 Set sample rate 48000, clock 0
usb 3-1: [5] FU [PCM Playback Switch] ch = 1, val = 0/1/1
usb 3-1: cannot set ctl value: req = 0x4, wValue = 0x200, wIndex = 0x500, type = 4, data = 0x80/0x0
usb 3-1: [5] FU [PCM Playback Volume] ch = 1, val = -12288/0/256
input: bestechnic Xiaomi Speaker Mini-2421 as /devices/pci0000:00/0000:00:08.3/0000:67:00.0/usb3/3-1/3-1:1.2/0003:2717:5096.002A/input/input69
hid-generic 0003:2717:5096.002A: input,hidraw10: USB HID v1.11 Device [bestechnic Xiaomi Speaker Mini-2421] on usb-0000:67:00.0-1/input2

(**** is the last four digits of the device's serial number)

Signed-off-by: Rong Zhang <i@xxxxxxxx>
---
sound/usb/mixer_quirks.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 69 insertions(+)

diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index 6cdd3ee94d66..3534f6fad74b 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -4840,6 +4840,71 @@ static void snd_ab13x_quirks(struct usb_mixer_interface *mixer, struct usb_mixer
}
}

+static void snd_xiaomi_speaker_mini_quirk_db_scale(struct usb_mixer_interface *mixer,
+ struct usb_mixer_elem_info *cval,
+ struct snd_kcontrol *kctl)
+{
+ /*
+ * Volume mapping based on normalized microphone measurement @ 1000Hz:
+ * +--------+--------+-----------+-------------+--------+
+ * | hex | dec | dec => dB | measured dB | res |
+ * +--------+--------+-----------+-------------+--------+
+ * | 0xd000 | -12288 | -48.00 | (mute) | |
+ * | 0xdd00 | -8960 | -35.00 | -68.6 | 3328 # |
+ * | 0xe540 | -6848 | -26.75 | -61.2 | 2112 |
+ * | 0xea40 | -5568 | -21.75 | -57.0 | 1280 |
+ * | 0xed80 | -4736 | -18.50 | -52.5 | 832 |
+ * | 0xf0a0 | -3936 | -15.38 | -48.3 | 800 |
+ * | 0xf2d0 | -3376 | -13.19 | -42.1 | 560 |
+ * | 0xf4d0 | -2864 | -11.19 | -36.1 | 512 |
+ * | 0xf6c0 | -2368 | -9.25 | -32.0 | 496 |
+ * | 0xf840 | -1984 | -7.75 | -24.0 | 384 |
+ * | 0xf9e0 | -1568 | -6.13 | -17.9 | 416 |
+ * | 0xfb30 | -1232 | -4.81 | -13.9 | 336 |
+ * | 0xfc80 | -896 | -3.50 | -10.0 | 336 |
+ * | 0xfd90 | -624 | -2.44 | -6.0 | 272 |
+ * | 0xfeb0 | -336 | -1.31 | -4.0 | 288 |
+ * | 0xffb0 | -80 | -0.31 | -2.0 | 256 |
+ * | 0x0000 | 0 | 0.00 | 0.0 | 80 |
+ * +--------+--------+-----------+-------------+--------+
+ *
+ * The volume control mixer declares res == 256, but actually acts like
+ * res == 1 (i.e., accepts any value between min and max) and has uneven
+ * resolutions in reality. Setting any value between (0xd000, 0xdd00]
+ * results in the same audible volume as 0xdd00, and so on.
+ *
+ * Footnote #: running out of the 10-item limit of TLV ranges.
+ */
+ static const DECLARE_TLV_DB_RANGE(scale,
+ 0, 0, TLV_DB_SCALE_ITEM( -6120, 0, 0), /* -7104 */
+ 1, 5, TLV_DB_SCALE_ITEM( -5700, 0, 0), /* -6808, -6512, -6216, -5920, -5624 */
+ 6, 8, TLV_DB_SCALE_ITEM( -5250, 0, 0), /* -5328, -5032, -4736 */
+ 9, 10, TLV_DB_SCALE_ITEM( -4830, 0, 0), /* -4440, -4144 */
+ 11, 12, TLV_DB_SCALE_ITEM( -4210, 0, 0), /* -3848, -3552 */
+ 13, 14, TLV_DB_SCALE_ITEM( -3610, 0, 0), /* -3256, -2960 */
+ 15, 16, TLV_DB_SCALE_ITEM( -3200, 0, 0), /* -2664, -2368 */
+ 17, 18, TLV_DB_MINMAX_ITEM(-2400, -1790), /* -2072, -1776 */
+ 19, 21, TLV_DB_MINMAX_ITEM(-1390, -600), /* -1480, -1184, -888 */
+ 22, 24, TLV_DB_MINMAX_ITEM( -400, 0), /* -592, -296, 0 */
+ );
+
+ if (cval->min == -12288 && cval->max == 0 && cval->res == 256) {
+ if (!deconflict_playback_tlv_quirks(mixer, kctl))
+ return;
+
+ /*
+ * These values are carefully chosen so that volume steps with
+ * 2dB or 4dB resolution can be approximately represented
+ * togother.
+ */
+ snd_usb_apply_db_scale_val(mixer, cval, kctl, scale,
+ "Xiaomi Speaker Mini", -7104, 0, 296);
+ } else {
+ usb_audio_dbg(mixer->chip,
+ "not applying Xiaomi Speaker Mini quirk on unknown variant\n");
+ }
+}
+
static void snd_usb_mv_silicon_quirks(struct usb_mixer_interface *mixer,
struct usb_mixer_elem_info *cval,
struct snd_kcontrol *kctl)
@@ -4915,6 +4980,10 @@ void snd_usb_mixer_fu_apply_quirk(struct usb_mixer_interface *mixer,
if (unitid == 7 && cval->control == UAC_FU_VOLUME)
snd_dragonfly_quirk_db_scale(mixer, cval, kctl);
break;
+ case USB_ID(0x2717, 0x5096): /* Xiaomi Speaker Mini */
+ if (cval->control == UAC_FU_VOLUME)
+ snd_xiaomi_speaker_mini_quirk_db_scale(mixer, cval, kctl);
+ break;
}

if (cval->control == UAC_FU_VOLUME &&

--
2.55.0